Black medic
Medicago lupulina

Habitat: Grassland, pastures, vegetable and agronomic crop fields (especially alfalfa), orchards, vineyards, gardens, lawns, roadsides and other disturbed, unmanaged places.
Seedling: Cotyledons (seed leaves) are oblong, smooth, and about 1/6 to 1/3 of an inch (4–9 mm) long. The first leaf is oval and broader than it is long, with a smooth edge. True leaves are fully subdivided consisting of three egg-shaped leaflets with toothed edges and resemble leaves of the mature plant.
Mature plant: The main stem branches near the base. Stems grow prostrate or prostrate with tips pointing upward and can reach 1-1/3 feet (40 cm) long. The plant is hairy, especially the stems. Leaves are alternate to one another along the stem. Leaves are fully divided into three egg- to heart-shaped leaflets with somewhat toothed edges. Leaflets are about 2/5 to 7/10 of an inch (1–2 cm) long and finely toothed at the tip, which often bares a tiny, slender tooth. The stalk of the middle leaflet is longer than those of the lateral leaflets. Black medic is distinguished from California burclover by its hairy leaves; the latter has nearly hairless leaves. Also the small leaflike structures (stipules) at the bases of leaf stalks are not deeply lobed and have smooth edges or a few shallow teeth in black medic, whereas those of California burclover are deeply lobed, slender and curved.
Flowers: Flowers bloom from April through July. Usually ten to twenty yellow, slender, pealike flowers densely cluster to form a rounded flower head.
Fruits: Fruits are kidney-shaped pods about 1/12 to 1/8 of an inch (2–3 mm) long, strongly veined, and black at maturity. Each pod contains one seed, but does not open to release seeds.
Seeds: Seeds are oval to barely kidney shaped, smooth, yellowish to olive green, about 1/12 of an inch (2 mm) long, and have a small sharp point on the concave side.